This invention relates to a battery switching device loaded on a vehicle such as an automobile to transmit an emergency radio signal in case of emergency, and an emergency call system using the same. More specifically, the invention relates to an improvement to enable the emergency radio signal to be transmitted by switching the main battery of the vehicle to an auxiliary primary battery.
FIG. 1 is a schematic diagram showing the configuration of a conventional battery system loaded on a vehicle such as an automobile. In the drawing, a reference numeral 45 denotes a main battery; 46 an auxiliary battery; 47 a switch for switching the batteries; 48 a vehicle driving system; 49 a residual quantity detection system; and 50 a display device.
Next, the operation of the conventional battery system will be described.
Normally, the switch 47 connects the main battery 45 to the vehicle driving system 48 or the like. The residual quantity detection system 49 detects the voltage of the main battery 45, and the display device 50 displays the voltage value thereof. When the output voltage of the main battery 45 drops down to below a predetermined voltage, the switch 47 connects the auxiliary battery 46 to the vehicle driving system 48 or the like, instead.
As the conventional on vehicle battery system is constructed in the foregoing manner, various inconveniences may occur when power is supplied from this battery system, and an emergency call device for transmitting an emergency radio signal in case of emergency is loaded.
The emergency call device generally comprises an emergency radio signal generation circuit for generating an emergency radio signal, and a transmitter section for transmitting the thus generated emergency radio signal by radio. The emergency radio signal generation circuit is operable if a voltage applied thereto is equal to or higher than a minimum operating voltage required for its operation. The transmitter needs a voltage equal to or higher than a minimum operating voltage required for its operation. Accordingly, when power is supplied to such an emergency signal transmitter by using the conventional battery system, the switch 47 must be set to be switched by a voltage at least equal to/higher than the minimum operating voltage of the transmitter.
In the case of a vehicle such as an automobile, however, an output voltage of the main battery 45 is typically set at 12 V and, since a large quantity of current is consumed, for example at the time of starting an engine, the voltage of the main battery is greatly reduced. Consequently, if a switching voltage of the switch 47 is set at 9 V, then switching may frequently be made from the main battery 45 to the auxiliary battery 46, leading to a wasteful consumption of power of the auxiliary battery 46.
Especially, there has been a problem inherent in the auxiliary battery 46. That is, although a non-chargeable primary battery is used for the auxiliary battery 46, as it can be used in the wide range of temperature, yet realizing low cost, if switching is made too frequently to the auxiliary battery 46, the primary battery must be replaced by another one even if no emergency call devices are used originally, which places a cost burden on an end user.
The present invention was made to solve the foregoing problems, and it is an object of the invention to provide a battery switching device capable of transmitting an emergency radio signal from an emergency signal transmitter by effectively suppressing the wear of an auxiliary primary battery, thereby preventing any cost burdens from being placed on an end user, and making sure switching from a main battery to the auxiliary primary battery in case of emergency. It is another object of the invention to provide an emergency call system using such a battery switching device.
In accordance with the present invention, there is provided a battery switching device, which is loaded on a vehicle and adapted to supply power from a main battery or an auxiliary primary battery of the vehicle to an emergency signal transmitter for transmitting an emergency radio signal. The battery switching device comprises: a first voltage detection circuit for detecting whether or not an output voltage of the main battery is lower than a first detection voltage for making operable an emergency radio signal generation circuit of the emergency signal transmitter; a second voltage detection circuit for detecting whether or not an output voltage of the main battery is lower than a second detection voltage for making operable a transmitter section of the emergency signal transmitter; a manual switch for outputting an operation signal; a trigger generation unit for switching made to output a trigger signal when the operation signal and/or an air bag starting signal is entered; and a switching determination circuit, to which output signals are entered from said first and second voltage detection circuits and said trigger generation unit, wherein said switching determination circuit always switches from the main battery to the auxiliary primary battery when an output voltage of the main battery lower than the first detection voltage, and switches from the main battery to the auxiliary primary battery only when a trigger signal is entered in a case in which an output voltage of the main battery is equal to or larger than the first detection voltage and lower than the second detection voltage.
With the battery switching device thus constructed, no automatic switching is executed from the main battery to the auxiliary primary battery unless the first detection voltage becomes lower than the second detection voltage. Thus, unnecessary switching to the auxiliary primary battery is prevented at the time of starting an engine or the like. It is therefore possible to effectively suppress the wear of the auxiliary primary battery, and to prevent any cost burdens more than necessary on an end user.
Further, when the first detection voltage becomes lower than the second detection voltage, switching is automatically made from the main battery to the auxiliary primary battery. In addition, a voltage lower than the second detection voltage and equal to or higher than the first detection voltage, the main battery is immediately switched to e auxiliary primary battery by operating the manual switch. Therefore, it is possible to transmit an emergency radio signal from the emergency signal transmitter by surely switching from the main batter to the auxiliary primary battery in case of emergency.
According to the battery switching device of the invention, the first voltage detection voltage circuit and/or the second voltage detection circuit determines whether or not an output voltage of the main battery is lower than each detection voltage by using the respective detection voltages, and determines whether or not an output voltage of the main battery is higher than the respective detection voltages by using each releasing voltage higher than the detection voltage.
Thus, compared with the case of using a signal voltage, the use of the detection voltage of the main battery and the releasing voltage prevents frequent switching in the vicinity of the first detection voltage and/or the second detection voltage. It is therefore possible to suppress the wear of the auxiliary primary battery.
According to the battery switching device of the invention, an accessory switch detection circuit is provided for detecting an operation state of an accessory switch of the vehicle. The switching determination circuit executes switching to the auxiliary primary battery only when accessory switch is being operated in the accessory switch detection circuit.
Thus, for example even when the main battery dies due to the lighting of a head light during an engine stop, since no switching is executed to the auxiliary primary battery, it is possible to prevent the wear of the auxiliary primary battery.
In accordance with the invention, there is provided an emergency call system, comprising: a main battery; an auxiliary primary battery; an emergency signal transmitter including an emergency radio signal generation circuit for generating an emergency radio signal, and a transmitter section for transmitting the emergency radio signal by radio; the above-described battery switching device for supplying power from the main battery or the auxiliary primary battery to the emergency signal transmitter; and a third battery for supplying power to the battery switching device.
With the emergency call system thus constructed, even when an output voltage of the main battery drops to lower than the first detection voltage, the battery switching device can be surely operated to switch to the auxiliary primary battery. Moreover, since the battery switching device is operated by the third battery provided separately from the auxiliary primary battery, it is possible to execute the switching without any wear of the auxiliary primary battery.